Rhodium Complexes Based on Phosphorus Diamide Ligands:  Catalyst Structure versus Activity and Selectivity in the Hydroformylation of Alkenes

Abstract

The rhodium-catalyzed hydroformylation reaction of 1-octene with phosphorus diamide ligands has been investigated. Four monodentate phosphorus diamide ligands and six bidentate phosphorus diamide ligands derived from a 1,3,5-trisubstituted biuret structure have been synthesized. These types of ligands combine steric bulk with π-acidity. The rhodium complexes formed under CO/H 2 have been characterized by high-pressure spectroscopic techniques. Spectroscopic experiments revealed that the monodentate ligands form mixtures of HRhL 2 (CO) 2 and HRhL(CO) 3 . The ratio HRhL 2 (CO) 2 :HRhL(CO) 3 depends on the ligand concentration and its bulkiness. The bidentate ligands form stable, well-defined catalysts with the structure HRhL∩L(CO) 2 under hydroformylation conditions. Both monodentate and bidentate ligands have been tested in the hydroformylation reaction of 1-octene. The monodentate ligands form very active catalysts, but the linear-to-branched ratio of the product is low. The bidentate ligands show improved selectivity compared to the monodentate ligands and an activity that is only slightly lower.

Synthesis of new calix[4]arene‐based phosphorus ligands and their application in the Rh(I) catalyzed hydroformylation of 1‐octene

“…Catalysts based on calix [4]arene-containing phosphorus diamide groups exhibited superior activity in comparison to the corresponding phosphites. This result confirms reports in the literature on effects obtained by the use of simpler phosphorus diamide and phosphite ligands [20]. Compared to the corresponding monomeric ligand, in several cases calix [4]arene-containing phosphorus diamide groups exhibited even higher efficiency and selectivity.…”

“…The comparison of the results obtained with catalysts based on 1 and the monomeric ligand 6 indicates that the assembly of four ligating phosphorus diamide groups in the calix [4]arene structure does not disadvantageously affect the yield as well as the selectivity of the reaction. This is in contrast to related investigations of van Leeuwen and coworkers, who observed a remarkable loss of activity by replacement of monodentate by the corresponding bidentate ligands [20]. Compared to catalysts based on calix [4]arene biuret ligands, the hydroformylation with phosphites 2, 4, and 7 is much more sensitive to the structure of the ligands and conditions applied.…”

“…Van Leeuwen et al [20] suggested that they are electronically closely related to phosphites. However, the biuret group was considered to be a better electron acceptor than two aryloxy groups.…”

Catalytic Markovnikov and anti‐Markovnikov Functionalization of Alkenes and Alkynes: Recent Developments and Trends

“…[34] In the hydroformylation of 1-octene, high activity but only moderate selectivity (up to 61 % n-nonanal) is obtained by using a monodentate ligand, though it exclusively forms a hydride complex in which the phosphorus ligands are coordinated in the equatorial plane. [35] Bidentate biuret ligands, which form stable catalysts of the type [RhH(CO) 2 LÀL] show improved selectivity (up to 86 % n-nonanal) compared to the monodentate ligands.…”

Synthesis and Reactivity of Group 6 and 10 Complexes of the Bis(dialkylaminophosphanyl)imineiPrN=C[CH2P(NiPr2)2]2

“…[2] This is due, in part, to the ease with which phosphorusϪheteroatom bonds can be formed, as exemplified by PϪO and PϪN moieties. Diaminophosphanes have been targeted for study as they exhibit enhanced σ-donor strength (basicity) when compared with arylphosphanes and even triaminophosphanes, yet are often more easily prepared than strongly basic alkylphosphanes.…”